1. Field of the Invention
The invention relates to an equalizer, and in particular relates to an audio graphic equalizer.
2. Description of the Related Art
A graphic equalizer typically comprises a number of band pass filtering functions residing in bands across a frequency spectrum. In the case of a graphic equalizer operating on audio signals, the frequency spectrum extends from a lower end of about 20 hertz (Hz) to an upper end of around 20,000 Hz; a spectrum comprising a typical person's audible range. A typical graphic equalizer segments the frequency band into a number of bands with center frequencies and boundary frequencies. For each of these bands, the graphic equalizer will either boost the signal or cut the signal, depending upon user inputs. By selectively varying the magnitude of an audio signal across the frequency band, the graphic equalizer may be used to reduce noise components, compensate for acoustical shortcomings, and even be used to compensate for user preferences in signal production. Acoustical shortcomings may include non-ideal room acoustics, amplifiers, microphones, and music reproduction equipment such as record and audio cassette tape players.
However, the filtering characteristics of a graphic equalizer often distort desired control parameters provided by a user and cause the graphic equalizer to have a filter function that does not accurately represent the desired control parameters. Meanwhile, each of the band pass filters not only varies signals in its own band but also adjacent bands. Because of the interband effect the band pass filters have on adjacent bands, the performance of all the bands becomes skewed. The interband effect the band pass filters have on adjacent bands is often called band coupling. Band coupling often results in greatly exaggerated or reduced filter performances in a particular band as compared to user input settings. The frequency response is not desired and distorted.